1. Field of the Invention
This invention relates to nanophotonic devices and particularly to silicide thermal heaters for silicon-on-insulator nanophotonic devices.
2. Description of Background
Control and switching of the operating parameters of arbitrary silicon-on-insulator (SOI) nanophotonic devices is possible by changing the temperature of the silicon waveguide in which the light is guided. A small change in temperature can induce a change in the refractive index of the silicon waveguide via the thermooptic effect, altering the effective optical length, permitting sensitive control over the manner in which light travels through the device. The temperature of any SOI photonic device may be changed locally by fabricating a metallic thin film resistive heater on or near the device itself. By passing a current through a thin film resistor, the temperature of both the resistor and the adjacent SOI device increase in proportion to the electrical power dissipated.
Thermal control of SOI nanophotonic devices is particularly relevant in application to optical circuit switched networks, where low power thermal ON-OFF switching with very low insertion loss is required. While thermally actuated silicon photonic devices have been previously studied, the past implementations suffer from a number of problems, the greatest being that they require processing which is incompatible with standard modern CMOS device manufacturing (choice of metals and liftoff deposition technique). Additional drawbacks of previous thermal heaters designs also include:
Exceedingly large footprint, with very wide heater stripes in comparison with nanophotonic waveguide dimensions, i.e. >10 μm;
Low thermal efficiency and large switching power, due to large heated area and large required power for inducing required temperature change at waveguide;
Excessively high switching voltage (>100 V required to pass current directly through silicon waveguide due to high series resistance) and large free carrier induced ON-state loss in the case of passing current directly through the silicon waveguide; and
Slow response time, due to inefficient transport of heat through non-conductive oxide films surrounding the waveguide.
The following is a discussion of some structures known to Applicant but which are not necessarily prior art to the claimed invention and their being mentioned is not an admission of prior art status. Referring to FIG. 1, there is shown a structure 100 with a stripped waveguide 102. A heater 104 is included in a separate piece of material that is in contact with the buried oxide layer 106. In FIG. 2, a heater is located directly above a buried oxide layer in which the silicon waveguide is embedded. FIG. 3 illustrates an approach where cladding provides heat to a silicon waveguide that is vertically disposed on a substrate. FIG. 4 shows a metal heater on a buried oxide layer. This has the shortcoming that it is not CMOS compatible.
For these reasons, novel solutions to the above problems are required before thermally controlled SOI nanophotonic devices become practical within large scale integrated optical circuits.